Tony,

I think they will perish if planted in open garden beds.
Last year lost the only two bulbs I had of Hippeastrum evansiae which were
housed in a roofed shade house during winter in zone 10. The winter wasnt
particularly cold (zone 10 - warm temperate conditions) with a minimum in
winter of 2 degrees centigrade.

I have also grown seedlings of evansii primary hybrids to flowering stage in
garden beds - but noticed that they also remain susceptible to colder winter
spells (-3 degrees), and most have perished since flowering.

Cheers

Jim Lykos